There are many occasions within a can manufacturing plant in which a mass of containers needs to be fed into a single line for supplying the containers to decorators, base coaters and other apparatus in the plant which must perform an operation on or with respect to the container. With the development of higher speed apparatus for performing all of these functions, it becomes necessary to develop apparatus for providing the containers to the equipment at greater speeds. Single filing used to be done by a variety of mechanical single filers. With the development of air conveyors, single filing devices have been developed which support the containers on a layer of air and use air as a propelling force for manipulating and moving the containers. This has provided significantly higher single filing capabilities.
One such single filing apparatus is disclosed in my U.S. Pat. No. 4,462,720 for .cent.Air Table System". This device supports containers on a table by a layer of air provided by air jets slanted in the downstream direction toward a single file conveying zone. An imperforate cover is placed above the surface of the table a distance slightly greater than the longitudinal dimension of the containers being transported and is positioned over at least a portion of the single file conveying zone. Blow-back jets are connected to a source of air under pressure for supplying air in the single file conveying zone in opposition to the direction of normal flow of the objects. By use of this apparatus, a mass of containers can be rearranged into single file arrangement for discharge at the downstream end of the table.
Another single filer is shown in my U.S. Pat. No. 4,561,806 for "Vertical Single Filer Conveyor System". In this apparatus, containers are fed from a mass of containers onto a table which has at least three zones extending from an upstream location. The containers are supported and moved by a prearranged pattern of flotation air jets. In addition, a row of acceleration jets, which are larger in size than the flotation jets, are located in the table adjacent to and spaced in parallel relation to converging sides of the table to form two converging rows of acceleration jets. Means is provided to incrementally increase the volume and velocity of air through the acceleration jets between each of the three zones from the upstream location to the downstream location to accelerate and longitudinally separate the objects as they move along the table from the upstream location to the downstream location so that the converging of the sides coacts with the acceleration jets to converge longitudinally separated containers in a prearranged pattern to bring them into single file. This device has been found to be very satisfactory for placing smooth decorated containers in single file at relatively high speed.
Neither of these devices will work with highly etched containers. During the manufacturing process, the containers are run through an acid wash which etches the outer surface of the containers so that the decorative coating will adhere to the surface of the containers. Furthermore, because of environmental concerns, the acid cannot freely be dumped, and therefore it is impossible to control the amount of etching on the containers as was previously possible. In other words, the acid solution must be strong enough to provide the minimum etching required but if there is a stall in the line and the containers stay in the etching solution too long the acid cannot be dumped but rather the container just becomes more highly etched. This creates greater problems in manipulating the containers because the adjacent contacting edges of the etched containers act like little gear teeth and interlock with each other so that the containers want to rotate with each other rather than moving individually and sliding past each other.
Still another single filer is shown in my U.S. Pat. No. 4,730,956 for "Shock Absorbant Single Filer". In this apparatus, multiple rows of containers are brought into an alignment zone, arranged in nested relationship, merged into a equilateral triangle configuration with mutually touching side edges in a nesting section within the alignment zone and accelerated into a high pressure buffer section of the alignment zone where they are separated from each other and converged into single file. In one embodiment, the imperforate side walls in the buffer section slope downwardly away from an imperforate top cover to provide gradual relief of air pressure within the buffer section. In another embodiment, the imperforate side walls have an upper edge which is contiguous with a top cover in the form of a plenum having rows of jet openings positioned above the jet openings in the air table. The imperforate side walls extend downstream to a point where the air buffer zone is less than two container diameters in width. The containers provide a self-valving action wherein the most downstream container moves away from the imperforate side wall on one side wall on one side and relieves the air pressure so that the next upstream container moves downstream. While this device is suitable for its intended purpose, it is of complex construction and requires adjustable dampers in both the upper and lower plenums for controlling and adjusting the air pressure on the containers.